Fiber Optics Connectors [telecom]


I need to read up on fiber optics connectors.

I'm familiar with the LC, ST, and SC type connectors.

I understand that there are special connectors called APC (Angle Polished Connectors) and I'd like to read up on when they are used.

Can someone recommend a book that explains APCs and some of the newer connectors [those I have not listed here]?



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Those are the 3 [most widely used] used ones. ST is not used much now. FC was used a lot by Qwest and other ILECs for SONET, but not so much now-a-days, being more SC types in newer installations.

That isn't a type of connector, but a style of end join. There are APC, UPC and straight. APC actually stands for Angled Physical Contact (not connector).

The point of the APC is that the ends are angled instead of flush, so when they mate, if there is any side glancing back reflection from the polished end that it bounces off to the cladding and only straight through signal gets pushed through. Kind of a bear to line up correctly, so they really only get used in FC type connectors that have a notch to line up the ferrule.

Unlike what Wikipedia says, I was taught that UPC polish on the end has just a slight curve to it and not just a better "polish", with just the signal path kissing just right in the middle. Same concept as the APC, just done more subtle and circular so it doesn't require mating the angle just right so any connector can be used (ie. SC) Plus if you mate UPC with straight cable, nothing bad happens. APC end to anything else will either break things, or have too large of a loss.

It costs just slightly more at the fiber assembly vendor to get UPC polish.

Typically in telco/datacenter applications, you'll get single-mode duplex, SC connectors with UPC polish. Ie. my cable vendor doesn't even ask, that is just what I get. Or if it a patch going from one piece of gear to gear without a patch panel in the middle, it'll be an LC to LC cable.

I haven't actually seen any installation with APC polished ends, but have heard that there are some out there local to me.

Not enough material for a book. And nothing else "new".

Wikipedia does a decent enough job.

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Otherwise, talk to a cable vendor (ie. Graybar, Anixter). Their sales critters should be versed enough in it as well.

Typically now-a-days, *everything* is SC and LC.

You still see the occasional FC from the ILEC panels. MT-RJ died off along with 100-Base-FL. ST died out earlier, but was installed in a *lot* more places. SMA and FDDI are long dead.

If you end up needing any other style, you just get the proper patch cable and leave it at that. It isn't like everything has to be the same all the way through.

***** Moderator's Note *****

100BaseFL died? Is multi-mode fiber still in use?

I remember a job I did to get a LAN across an isolated ground window: fiber transceivers and ST connectors saved me a _lot_ of grief.

Bill Horne Moderator

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Doug McIntyre

I guess in my environment (telco/datacenter), anything new going in is probably going to be 10Gbit. With a smaller percentage of Gigabit ethernet (at whatever standard for fiber related, 1000-Base-SX or

1000-Base-LX or 1000-Base-ZX). Guess I'm not large enough to see any 40G and 100G installations.

I haven't seen 100Mbps fiber at 100-Base-FL for maybe 9-10 years now. The switch to gigabit was pretty instant once things there became afordable for almost everybody. The sweet spot for 10Gbps is still in the telco/datacenter realm. Smaller enterprises are probably still on gigabit or LAG'd gigabit. I can buy GigE switches with a few fiber ports for low $200's now-a-days.

Yes, multi-mode fiber is still in use. I just installed 100m of OM3 MM (with SC connectors) which is what is needed to run 10Gbase-SX on multi-mode fiber. (50um core, "laser-optimized" fiber).

Although I know several places that don't bother figuring out of they want multi-mode or single-mode and just standardize on single-mode fiber, as the gear and material prices aren't that much higher (ie. $200 for a 10Gbase-SX SFP vs $500-$600 for a 10Gbase-LX SFP).

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Doug McIntyre

All three of those use 2.5mm ferrules (the little pointy part of the connector) and are used for cross connections at fiber panels and some equipment ports. ODC (Outdoor Connector) is another 2.5mm ferrule connector, but not one I've worked with. More and more vendors are using 1.25mm ferrule connectors such as LC or MU (less common) to allow greater port densities. MTP/MPO connectors also show up. Those terminate ribbon fibers composed of several separate fibers in a single connector.

And of course there are many older and niche connectors out there.

This is one of those acronyms that depend on who you're talking to. Even fiber vendors use both. Either one works and refers to the same thing.

APC is superior to UPC as far as return loss from the connector. Both types have back reflection due to the transition of material from the core through the connectors but APC minimizes as described above due to the angled surface. I mostly use APC in SC & MTP connectors but according to TE (formerly ADC) it's available in LC connectors too. Neither SC or MTP is difficult to mate because the connectors only come together one way. Inspection probes allow the ferrule to rotate but there's a mark on it to line up the correct angle.

It's also not that big of angle, 8 degree slant for APC versus 0 degree for UPC.

More on the differences from ADC here:

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